The present invention relates to engine analyzer apparatus used for testing internal combustion engines. In particular, the invention relates to a waveform display for an engine analyzer apparatus.
One common type of engine analyzer apparatus used for testing an internal combustion engine employs a cathode ray tube having a display screen on which analog waveforms are displayed which are associated with operation of the engine. In a typical apparatus of this type, a substantial horizontal trace is produced on the screen of the cathode ray tube by applying a sawtooth ramp voltage between the horizontal deflection plates of the tube while the analog signal being measured is applied to the vertical deflection plates of the tube. The typical analog signals which are applied to the vertical plates of the cathode ray tube are the primary voltage which exists across the primary winding of the ignition coil, and a signal representative of the secondary voltage of the ignition coil. These voltages are affected by the condition of various elements of the ignition system of the engine, such as the spark plugs.
In the case of a multicylinder internal combustion engine, the primary and secondary voltage waveforms have typically been displayed on the cathode ray tube in one of two ways. In one case, the waveform being displayed represents a complete cycle of the engine, in which the conditions associated with the various cylinders are displayed sequentially in a predetermined pattern. This type of display has commonly been referred to as a "parade" pattern or display.
In the other common method of displaying waveforms, there are a plurality of horizontal traces, one above the other, with each trace being associated with the operation of one of the cylinders of the engine. The number of horizontal traces usually corresponds to the number of cylinders on the engine. This method of displaying waveforms has been referred to in the industry as a "raster" display.
With the advent of low cost microelectronic devices, and in particular microprocessors, digital electronic systems have found increasing use in a wide variety of applications. Digital electronic systems have many significant advantages over analog systems, including increased ability to analyze and store data, higher accuracy, greater flexibility in design and application, and the ability to interface with computers having larger and more sophisticated data processing and storage capabilities. In the past, it has been difficult to display the waveform for an engine if engine speed changed during the sampling period. For example, U.S. Pat. No. 4,399,407 issued to Kling et al. on Aug. 16, 1983 and entitled ENGINE ANALYZER WITH CONSTANT WIDTH DIGITAL WAVEFORM DISPLAY, incorporated herein by reference, is one such method in which the waveform of each cylinder is adjusted to have equal width when displayed.
Prior art display techniques have required two complete engine cycles for each display. During a first timing cycle, timing information is collected which is used to determine the sampling rate for each cylinder. Variation in the speed of the engine between the timing cycle and the data collection cycle could result in loss of data in the waveform of a cylinder.
A display technique in an engine analyzer system which displays the waveform for an entire firing cycle and which allows for comparison between time variations for cylinders of the engine would be a significant contribution to the art.